1. Field of the Invention
The present invention relates to a fixing structure of a link and a pin of a travelling crawler belt used for a crawler vehicle, and a fixing method thereof.
2. Description of the Related Art
As shown in FIG. 14, in a conventional crawler belt 1 used for a crawler vehicle of a construction equipment such as a bulldozer and a tractor, a plurality of crawler plates 2 to contact with the ground are mounted to an endless link chain 3 by bolts. The link chain 3 is assembled by sequentially press-fitting respective ends of left links 6 and right links 7 onto, for example, cylindrical bushes 4 and connecting pins 5 which are inserted into the bushes 4 such that opposite ends of the connecting pins 5 are exposed outside. The respective ends of the links 6 and 7 are connected to each other in a jointed manner by the pins 5 in a state in which the links 6 and 7 are spaced from each other.
At each of the ends of the links 6 and 7, there is disposed a non-illustrated sealing member which seals lubricant for preventing an internal friction between the pin 5 and the bush 4, and a non-illustrated spacer for preventing the sealing member from being crushed. The lubricant stored in the pin 5 is supplied to a space between the pin 5 and the bush 4.
The link chain 3 is generally used for travelling on the ground such as of sand, gravel, crushed stone, or soft ground, and ascent ground. Therefore, the link chain 3 is liable to receive external force applied to the links 6 and 7 in an axial direction thereof by, for example, flange of a lower roller of a non-illustrated vehicle body, or external force applied to an end surface of the pin 5 in an axial direction thereof by a roller guard of the vehicle body, or the likewise external force. For this reason, it is necessary to strongly press-fit the ends of the links 6 and 7 so that the pin 5 does not move in the axial direction by the external force. When a retaining force of the pin 5 is small, the pin 5 would be displaced or pulled out. Thus, the lubricant-sealing member and the crush-preventing spacer disposed at each of the ends of the links 6 and 7 would be deformed, displaced in positions, damaged or so on.
If the sealing member and the crush-preventing spacer for the sealing member are damaged or the like, the lubricant is consumed extremely. As a result, internal friction is generated between the pin 5 and the bush 4 and thus, the pin 5 and the bush 4 are rapidly damaged, so that the link chain 3 looses its original function. In order to prevent the pin 5 from being displaced in position or being pulled out, a large pressing margin Is usually secured to strengthen the fixation by the press-fit. However, since there is a limit to strengthen the fixation by the press-fit, it is necessary to employ a structure for mechanically preventing the pulling out of the pin 5 in addition to the press-fit of the links 6 and 7 with respect to the pin 5.
In order to overcome such problems, there have been developed a ring-type structure for preventing the pin from being pulled out, as shown in FIG. 15 for example, or a structure for preventing the pin from being pulled out as disclosed in Japanese Patent Laid-open No. 5-213237 as shown in FIG. 16. The former prior art employs a structure in which each pin 5 for connecting links has at its one end an annular groove 8, a C-shaped pulling-out-preventing member (not shown) is engaged with the annular groove 8 in a state in which the pin 5 abuts with each end of the links 6 and 7. According to the latter prior art, as shown in FIG. 16, each pin 5 has at its one end an annular groove 8 having an arc cross section. Portions of outer peripheries of bosses of the links 6 and 7 are pressed and deformed by punch devices 9 which are disposed radially around and opposing to the annular groove 8 so that small blocks are allowed to project into and engaged with the annular groove 8. In FIG. 16, a reference number 10 represents a lubricant-sealing member, and a reference number 11 represents a crush-preventing spacer for the sealing member 10.
Meanwhile, in general, the term of "pulling out of pin" means a phenomenon that a link is removed from the pin. When the link moves outside of the pin, a gap is made between the bush and the sealing member interposed between the bush and the link, so that the lubricant leaks out, thus the lubricating function is lost and the vehicle can not run.
A main reason that the "pulling out of pin" phenomenon occurs is a load in the above-mentioned axial direction applied to the link. Especially at the time of steering, movement of the pin is facilitated by external forces, in many directions, applied between the bush and a sprocket.
For this reason, even if the link moves relative to the pin, and a displacement of 1 mm is generated for example, the vehicle can not run as described above. On the other hand, a life span of the crawler belt may be determined by abrasion of the bush. This is caused by engagement between the bush and the sprocket, and only the engaged surfaces between the bush and the sprocket is worn out. Thereupon, in a state in which the bush is rotated with a predetermined angle relative to the link, a position of the bush where the bush is worn out most is displaced from the forward to the rearward in the circumferential direction, and the link is press-fitted and fixed again. At that time, the lubricant-sealing member is replaced with new one if necessary. With this operation, it is possible to substantially extend the life span of the bush.
However, in order to change the press-fit position of the bush and the link in phase in the circumferential direction, it is necessary to take out the link from the pin. Since a large press-fit margin is usually secured as described above so that the pin and the link are strongly press-fitted and fixed by a great press-fit force, a further greater pulling force is necessary for pulling out the link which is press-fitted and fixed to the pin, thus a great number of striped scratches are made on the press-fit surface of the pin and the link. Therefore, if the press-fit position of the pin and the link is to be changed in the circumferential direction, although the fixation strength is not essentially lowered, the striped scratches must be removed in many cases after the link is pulled out from the pin. By this removing operation, the press-fit strength tends to be rather lowered.
Thereupon, in addition to the general press-fit fixation of the pin and the link as described above, the mechanical pulling-out-preventing structure of the pin is further employed. In a case of the mechanical pulling-out-preventing structure shown in FIG. 15, since the C-shaped retaining members are retained to the respective ends of the links 6 and 7, it is necessary to align the ends of the links 6 and 7 with the annular groove 8 in position, so that high precision in size and complicated machining are required for the products. As a result, variation among the products is prone to be generated, so that the number of defective parts generated is not small. As a result, extra time and labor are required for assembling the respective links 6, 7 and the pin 5, so that the operation is prone to be complicated, and a certain skill is required for the assembling operation.
According to the above-described Japanese Patent Application Laid-open No. 5-213237, a thin link boss is pressed from outside to form a plurality of plastically deforming portions in the circumferential direction thereof, and the small blocks are projected in the annular groove 8 formed in the end of the pin 5 for retaining. Since the pressing operation is carried out only by locally punching the outer periphery of the boss in its diametrically-shrinking direction, the number of portions to be engaged with the pin 5 is small, and the projecting length and thickness of the engaged portion are small. Therefore, the force for retaining the pin 5 in the axial direction thereof is so small that the durability can not be expected. Thus, when the respective links 6 and 7 receive external force or the like in a thrust direction applied from a flange of a lower roller or a roller guard of the vehicle body as described above, the lubricant-sealing member 10 and the crush-preventing spacer 11 disposed in a joint portion of the links 6 and 7 tend to be damaged, likewise the conventional fixation merely by press-fit.
Further, since it is impossible to visually check the annular groove 8 of the pin 5 press-fitted to the boss of the links 6 and 7 from outside, there are problems that it is extremely difficult to reliably retain the small blocks projecting from an inner wall of the boss to the annular groove 8, so that it can not determine whether the small blocks are reliably engaged within the annular groove 8 not only during the assembling operation of the links 6, 7 and the pin 5, but also after the assembling operation. Further, since each boss projects from a side surface of the link, the boss is prone to interfere with outside obstructions, rocks and the like, thus rattle is prone to be generated.
Furthermore, it is necessary to dispose exclusive punching devices around the bosses in addition to the link press used for assembling the links 6, 7 and the pins 5. For this reason, the projecting amount of each boss must be set great, so that the cost of material, the cost of equipment and the manufacturing cost are increased. In addition to these, variation among products is prone to be generated and the number of defective parts is not small as compared with the fixing structure disclosed in the above mentioned Japanese Patent Laid-open No. 61-184178, thus the operation is prone to be complicated.